Process for vacuum distillation of hydrocarbon oils



H. c. wu-zss 1,786,639

PROCESS FOR VACUUM DISTILLATION OF HYDROCARBON OILS Dec. 30, 1930.

Filed Sept. 25 1925 ga 2gb TQM NNMKSQQEQU N in m HARRY C. \Almas gwuentoz 351 attic 044mg 45 allyy be operated at an absolute pressure not Patented Dec. 30, 1930 UNITED STATES PATENT OFFICE HARRY C. WIESS, OF HOUSTON, TEXAS, ASSIGNOR TO STANDARD OIL DEVELOPMENT COMPANY, A CORPORATION OF DELAWARE PROCESS FOR VACUUM DISTILLATION OF HYDROOABBON OILS Application filed September 25, 1925. 'Serial No. 58,501.

An auxiliary still 23 for the light hydro- This invention relates to improvements in processes for distillation of hydrocarbon oils under conditions preventing substantial decomposition. A feature of the present in vention is the utilization of a light hydrocarbon liquid, such as naphtha or gasoline, as an aid in distillation under pressure less than atmospheric.

The invention will be fully understood from the following description, taken in connection with the accompanying drawing, in which the single figure is a diagrammatic side elevation. partly in section, of an apparatus embodying the principles of the invention.

Referrin to the drawing, numeral 1 denotes a sti which may be of the conventional horizontal shell type, having a tower 2. The still may be arranged in a furnace setting 1a, or other suitable heating means may be rovided. Bafiies 3, bell-cap plates, or the 11 e, are provided in the tower 2 to minimize entrainment. A vapor line 4 leads to a fractionating column 5. The lower portion of this column is preferably filled with inert packing material 6. A tubular heat exchanger 7 is arranged in the upper portion of the column 5. Fluid for circulation about the tubes of the heat exchanger is introduced from a receptacle 8 through line 9 and passes out through line 10.

The column 5 is connected. near its top with a condenser 11 having a cooling jacket 12 and discharging through pipe 13 into a tank 14. Two or more receivers 15 and 16 are connected to receive reflux condensate from the column 5, which is connected with them through line 17. Tank 14 and receivers 15 and 16 are connected respectively by the valved lines 18, 19, and 20, to a line 21. A vacuum pump 22 in the line 21 maintains the entire s stem under reduced pressure. The pump should ordinarily be of sufficient capacity to maintain a high vacuum throughout'the system. The apparatus will usu- "#grj'ater than that corresponding to mm. of mercury, and for most purposes the pres sure will be reduced to between 5 and 25 mm. of mercury, or less.

carbon liquid to be used in the istillation is connected by pipe 24 with the main still 1. The pipe 24 preferably discharges into a header 25 with which arcuate perforated arms 26 communicate. The stilll is supplied through a pipe 27 with the oil to be distilled.

The following example is illustrative of the invention: The still 1 is char ed with residuum from heavy coastal cru e, heavy lubricating distillate, or similar stock adapted for the preparation of heavy lubricating oil. The still is fired to produce an oil temw perature therein of about 625 F., at which temperature the oilmay be expected to have a vapor pressure of about 5 mm. of mercury. A light hydrocarbon liquid, preferably naphtha, having a relatively narrow boiling range, for example between 350 to 425 F., is heated in the auxiliary still 23 to a temperature of 200 to 400 F. The important advantages that are secured by using naphtha of the type mentioned, or slmilar hydrocarbons, will be more fully described farther on. The fiue as from the furnace setting of the main still 1 may be used to heat the auxiliary still 23, or the still may be heated from the furnace setting supplied for it, as shown.

The vacuum pump 22 is put in operation and should maintain an absolute pressure on the system corresponding to not more than 25 mm. of mercury. The heated naphtha vapor is injected into the still 1 through the arcuate pipes 26 and passes up through the tower 2 with the vapors disengaged from the oil in the still. In preparing heavy lubricants under the temperature and pressure conditions stated it is desirable to inject the naphtha vapor at a rate per hour of about 2 gals. measured as liquid per sq. ft. of vapor disengaging surface in the still. These figures are given by way of example only; for higher oil vapor pressures the allowable injection rate is considerably greater. The rate may of course vary with particular conditions and can be determined for each case by measuring the amount of heavy condensate formed in column 5. If the rate of formation of heavy condensate is insufiicient, the naphtha in ection should be' 'increased. In order to avoid diiiiculty from entrainment or the like, the naphtha should not be in jected and vaporized so rapidly as to produce an ob'jectionably high linear velocity of vapor leaving the surface off the oil. The naphtha may be introduced as a cold or pre heated liquid into the still l and vaporized therein," but better results are ordinarily obtained by vaporizing the naphtha asin the auxiliary still 23.

When naphtha or its vapor is injected at the rate specified, or a similar rate, the necessary partial pressure of the oil undergoing distillation is reduced sufficiently to permit the taking off overhead of the desired heavy lubricant without increasing the tempera ture to a point at which cracking might take place.

Most of the entrained particles of oil are removed by the baffles 3, bell-cap plates, or

the like, in tower 2. The stream of vapors of naphtha and heavy oil enters the packed portion of the column 5, in which portion the heavier fractions of the distillate condense.

Such fractions may be drawn off continuously or intermittently to the receivers 15, 16. The lower portions of the column 5 may be heated by the burner 5, in case the heat of the vapors is not sullicient to expel substantially all the naphtha from the condensed product. Flue gases from the still 1 may be used as the heating means, if desired.

Steam is superheated in receptacle 8 and passed through line 9 about the tubes of the heat exchanger 7 to maintain a temperature sufficiently high to prevent condensation of naphtha. In the condenser 11 the temperature is lowered to a point at which the naphtha condenses. The condensed naphtha is collected in tank 14 for reuse in the process, or other disposition. The temperature of the naphtha in the tank may be about to F.; its vapor pressure will not exceed 25 mm. at that temperature.

The process may be operated upon a batch of oil, or the still 1 may be led continuously with the oil to be distilled.

As noted above, T prefer to use naphtha having a relatively high initial boiling point. Such naphtha has a vapor pressure materially lower than that of water at all temperatures to which a condensed distillation medium can be conveniently cooled in commercial installations. Maintenance of high vacuum is accordingly facilitated by the practice of this invention.

For example, if steam were used in the ap= paratus described, the cooling water supplied to the jacket 12 of the condenser 11 would not ordinarily bring the temperature of the condensed Water in tank i i much below 90 F. Water at this temperature has a vapor pressure of about 35 mm. The vapor pressure in the tank 14 imposes a limitation upon the reduction of vacuum throughout the whole system, so that in steam distillation the maximum vacuum corresponds to an absolute pressure greater than 35 mm. of mercury. While further cooling might be used to reduce the vapor pressure or the condensed water, this would ordinarily render the high vacuum process uneconomical.

In contrast with this, where naphtha of high boiling range is used, cooling tc 90 F. reduces the vapor pressure of the naphtha to from 5 to 10 mm. High vacuum may therefore be more easily maintained than in the case of steam distillation under comparable conditions. Also, less naphtha vapor than water Vapor is carried out through the vacuum pump with the incondensible gas from the system.

While naphtha of the specified boiling range is preferred, some of the advantages of the invention may be obtained by using any naphtha or gasoline consistin practically exclusively of constituents boiling Well above 212 F., that is, naphtha or gasoline having a materially lower vapor pressure than that of water at the temperature of condensation. Of course, when high vacuum is desired low boiling naphtha having a relatively high vapor pressure at the temperature of the condenser should not be used.

It will be understood that the specific process and apparatus described represent the preferred forms of the invention but are illustrative only. Various modifications and alternative arrangements may be made within the scope of the appended claims, in which it is my intention to claim all novelty inherent in the invention, as broadly as the prior art permits.

I claim:

1. Process of distilling hydrocarbon oil,

comprising heating the oil to a distillation temperature, injecting into the oil a li ht hydrocarbon, liquid under ordinary conditions, and having a vapor pressure less than that of water at the corresponding temperature of condensation, and reducing the absolute pressure upon the oil undergoing distillation to 50 mm. of mercury or less.

2. Process of distilling hydrocarbon oil, comprising heating the oil to a distillation temperature, reducing the absolute pressure upon the oil to 50 mm. of mercury or less, injecting into the oil, naphtha having a vapor pressure less than that of water at the corresponding temperature of condensation, taking off vapors of the oil and naphtha vapors together to a partial condensation zone, condensing vapors of the oil therein, withdrawing the condensate, taking off naphtha vapors, and condensing the same.

3. Process according to claim 2, in which the naphtha is preheated before injecting it into the oil.

4. In a process of distilling hydrocarbon oil at an absolute pressure not substantially exceeding 50 mm. of mercury and at a temperature not substantially exceeding 625 F., the step of introducing into the oil to be distilled naphtha composed substantially of constituents having a boiling point well above 212 F., and adapted to reduce the partial pressure of said oil sufiiciently to permit distillation thereof under the temperature and pressure conditions imposed.

5. Process of distilling hydrocarbon oil under high vacuum, comprising heating the oil to a distillation temperature, injecting into the oil naphtha having a boiling range between about 350 and 425 F., and reducing the absolute pressure upon the oil undergoing i distillation to 50 mm. mercury or less.

6. Process of distilling hydrocarbon oil under high vacuum, comprising heating the oil to a distillation temperature, injecting into the oil naphtha having a boiling range between about 350 and 425 F., taking ofif vapors of the oil and naphtha vapors together to a partial condensation zone, condensing vapors of the oil therein, withdrawing the condensate, taking off naphtha vapors, condensing the same at such a temperature that the vapor pressure of the condensed vapors does not exceed 25 mm. of mercury, and holding the absolute pressure on the oil undergoing distillation not to exceed 25 mm. of mercury.

HARRY C. WIESS. 

